Method for measuring liquid particle distribution from fogs clouds and sprays

ABSTRACT

A method for studying the size, number and distribution of droplets in fogs, clouds or sprays of the type produced by aerosols used in weather modification and the like.

United States Patent 1191 McEwan et a1. June 28, 1974 METHOD FOR MEASURING LIQUID PARTICLE DISTRIBUTION FROM FOGS, [56] References Cited CLOUDS, AND SPRAYS UNITED STATES PATENTS [75] Inventors: William S. McEwan, China Lake, 2,787,238 4/1957 Luce 116/114 AM Califi; Charles M. Drew, Redstone, 3,084,658 4/1963 Schell Colo, 3,221,428 12/1965 Fischler et a1" 3,740,196 6/1973 St h ff 23/253 TP [73] Assignee: The United States of America as row 0 represented the Secretary of the Primary Examiner-R. E. Serwin Navy washmgton Attorney, Agent, or Firm-R. S. Sciascia; Roy Miller; [22] Filed: Oct. 18, 1972 Lloyd E. K. Pohl [21] Appl. No.: 298,707 [57] ABSTRACT A method for studying the size, number and distribu- [52] 23/230 23/253 73/170 tion of droplets in fogs, clouds or sprays of the type Cl G01" 532 produced by aerosols used in weather modification [58] Field of Search 23/230 R, 23 0 c, 232 R, and the 23/253 R, 253 TP; 73/170 R; 116/114 AM 3 Claims, 2 Drawing Figures Ill/IIII/III'IIII Fig. l

fected when the fog,

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for use in weather modification studies. More particularly, this invention relates to a method for studying droplets from fogs, clouds and sprays.

2. Description of the Prior Art In weather modification programs and the like it is often desirable to determine the size, number and distribution of droplets in a given area of an aerosol fog, cloud or spray. Light scattering techniques are commonly used for this purpose. However, as a means for checking data obtained from light scattering techniques, other methods have been developed. These methods commonly involve the use of fallout meters of various shapes such as rotary plates, flat plates, etc., provided with slots to collect droplets of various predetermined sizes. These fallout meters utilize various collecting surfaces such as printflex paper, magnesium oxide coated slides, paper printed with indicating paint,

gelatin coated plates and waterproofed collection tape.

Each of the prior art collecting surfaces is adversely afcloud or spray contains a large amount of precipitation. A large amount of precipitation prevents the droplets from producing sharp marks or signatures on the collecting surface which truly represent the characteristics of free droplets.

As a more specific example, gelatin coated plates are commonly used in studying droplets from fogs, clouds or sprays. When certain aerosol sprays, such as ammonium nitrate/urea which is commonly utilized to disperse warm fog, strike gelatin the droplets tend to dif' fuse through the gelatin and do not give sharp outlines. Since the droplet size (volume) is directly related to the droplet diameter, a sharp outline is necessary. Therefore, gelatin coated plates are generally unsatisfactory for use in the study of ammonium nitrate/urea aerosols.

SUMMARY OF THE INVENTION In the present invention apparatus comprising a smooth metallic mirror on a substrate of suitable composition such as plastic or glass is used to study droplets from fogs, clouds and sprays. The identity of the metal used in the metallic mirror depends upon the composition of the droplets being studied.

The method of the present invention involves providing apparatus of the type generally described above, exposing the apparatus to a fog, cloud or spray for a predetermined length of time to cause droplets to adhere to the surface and form signatures, setting the signatures for a predetermined length of time and drying the surface of the apparatus with a drying agent. The signature containing apparatus can then be sealed in clear plastic to provide a permanent record.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross section view of apparatus suitable for studying ammonium nitrate/urea aerosols.

FIG. 2 is a cross sectional view of apparatus suitable for studying maritime fogs.

Going first to the drawing, FIG. 1 depicts, in cross section, a substrate 10 coated by known vacuum deposition methods with a single metallic film 11. In studying ammonium nitrate/urea aerosols the metallic film may be a metal such as copper, cadmium, zinc or the like. In use the metal coated substrate of FIG. I is exposed to an aerosol utilizing an ammonium nitrate/urea carrying agent to allow droplets from the aerosol to contract the metallic filin and adhere thereto. Contact may be accomplished by manually sweeping the device of FIG. I through a cloud of aerosol. Immediately after contacting the aerosol, the device with-droplets adher ing thereto is placed near an open container of acetic acid. Contact with fumes from the acetic acid causes the droplets to form signatures on the metallic filrh which correspond to the droplet diameters. Contact with the acetic acid fumes should be very brief on the order of 0.5 second to prevent corrosion of the metallic film. After contact with the acetic acid, the device is dried by rinsing in a drying agent such as ethanol to which a small amount of a base such as ammonia has been added to neutralize any acid in the ethanol.

FIG. 2 depicts a device similar to that of FIG. I with the exception that a second metallic film l2 coats the first opaque metallic film 11. As in FIG. 1, the substrate 10 may be either glass or plastic. The device of FIG. 2 is useful in studying maritime fogs and the two metallic films 11 and 12 are of two different metals. For study ing maritime fogs zinc (film 12) on either copper or cadmium (film 11) has been found to be satisfactory. In studies of maritime fogs it has been found preferable to limit the thickness of film 12 to about 200 angstroms or less. A thickness of 200 angstroms or less appears to leave minute holes in film 12 and allow traces of the droplets to contact film I1 and this produces more satisfactory results. On the other hand, film 11 in either FIG. I or FIG. 2 should be greater than 200'angstroms in thickness in order to completely prevent Contact be; tween droplets and substrate 10.

The method for using the device of FIG. 2 is the same as that for FIG. 1.

After'signatures have been set by placing a droplet containingdevice near a container of acetic acid and the device has been dried a permanent record may be made by coating the device with clear plastic.

We claim:

l. A method for determining particle distribution from fogs, clouds and sprays which comprises:

7 a. providing a device comprising a substrate coated on at least one side with at least one layer of metallic film;

b. depositing liquid particles on said film by exposing said device to particle containing air;

0. causing the liquid particles to form signatures which correspond to the droplet diameters on said film by placing said particle containing device near enough an open container of acetic acid to be in contact with fumes from the acetic acid for a predetermined length of time; and

d. drying the device by rinsing in a drying agent.

2. The method according to claim 1 wherein said substrate is coated with a first opaque layer of copper and wherein said copper layer is then coated with a film of zinc.

3. The method in accordance with claim 2 wherein said signature is set by placing the signature containing film coated substrate near a container of acetic acid for 

2. The method according to claim 1 wherein said substrate is coated with a first opaque layer of copper and wherein said copper layer is then coated with a film of zinc.
 3. The method in accordance with claim 2 wherein said signature is set by placing the signature containing film coated substrate near a container of acetic acid for about 0.5 second. 